Accessing stock Ubuntu console through UART

This question relates to connecting a USB UART bridge (FTDI, Silabs, Cypress, or any other) to a host computer with a display and using it to access a headless air gapped Up squared computer running the stock Ubuntu 16.04 LTS. One reason users do this is in order to discover or manipulate the network configuration on a headless Up squared computer.

How many

It seems that the Up squared computer has at least three UART interfaces, however it's unclear if all, some, or none of these are accessible from the Apollo Lake SoC.

Confirm

Please confirm the assumption that UART0 is accessible from the SoC and that it appears in the device tree (/dev/tty*) of the host OS.

Any others

How many (UART1, UART2, UARTn?) other UART interfaces exist, and do any of them appear in the device tree of the host OS?

FPGA

It seems from the published yet poorly detailed specification that the Altera Max 10 FPGA connectes to the Apollo Lake SoC over one or two UART interfaces. Do these interfaces appear in the host OS device tree, and if not then how are these UARTs intended to be used (aside from high level tools with lack of tranparency.)

Driver

I assume that Arduino Create environment uses the FPGA accessible UARTs to program the bitstream? Please confirm this and indicate if other command line toos exist that are able to connect to these UARTs and program the bitstream with no need for Arduino Create or other such Internet connected service.

Connectivity

To interface to UART0, is it advisable to plug a 1,27mm pin pitch cable into CN16? What is the pin assignment inside this white coloured connector, in other words which pins correspond with UART0-Rx and UART0-Tx?

Hat contacts

Why aren't any of the UART specifications numbered, are the indicated UART contacts on pins 8 and 10 short circuited to those in the 10 pin header connector CN16?

Conclusion

These documentation inadequacies are really confusing and leading to design errors and wasted time.